It is known in the art that electrochemical cells having an anode of lithium or other Group I metal have high energy densities, high voltages, wide temperature operating ranges, long shelf-life and relatively low cost.
In such cells, the type now commonly referred to as the liquid oxyhalide cell are of particular interest. These cells are described, for example in U.S. Pat. No. 3,926,669 and in British Pat. No. 1,409,307. In accordance with the teachings of the aforementioned patents, the electrolyte, which, together with the current collector, functions as the cathode, comprises an oxyhalide, for example thionyl chloride.
One attractive system is provided through the use of thionyl chloride, a solute of lithium aluminum tetrachloride, a lithium anode and a cathode current collector, which may be for example compressed carbon black. Despite the numerous advantages envisioned for lithium liquid oxyhalide batteries, it has been found that problems occur with these cells. A particular problem has been identified as that of voltage delay particularly occurring when the batteries are stored at elevated temperatures. The voltage delay problem is characterized by two features; to wit, a dip in voltage below a defined cutoff voltage and the time required for the voltage to rise back to the cutoff voltage. The problem is believed to result from passivation of the lithium anode due apparently to reactions between the lithium anode and constituents of the electrolyte.
In accordance with U.S. Pat. No. 4,170,693 it is proposed to minimize the voltage delay problem by coating the lithium anode with a cyanoacrylate polymeric coating.
In accordance with U.S. Pat. No. 4,296,185 it is proposed to minimize the voltage delay problem by inserting a cyanoacrylate sheet in the cell contiguous to and in physical contact with the anode. It is further taught in U.S. Pat. No. 4,296,185 that this sheet should remain intact and contiguous to the anode during cell operation while allowing lithium ions to pass through it.